[patwolf]

Having lived in rural areas, suburban areas, and urban areas, I don't see there being much difference in walking between rural and suburban.

My guess is that it's a combination of rural areas being poorer (less access to healthy food and extra curricular activities) and the lack of societal pressure to be healthy that comes from living in a more isolated environment.

[SauciestGNU]

I suspect if you closely examined activity levels by distance from city center, you'd see something like a log curve with moderate activity for city dwellers, decreasing as you get farther from the core, to the point where suburban/exurban/rural dwellers have very similar activity levels.

[strken]

I saw a huge difference when I moved from a tiny rural town to a city. I grew up comparatively close to a decent-sized town, in that it was a 20 minute bicycle ride or more than one hour walk to the nearest supermarket, but in the city I found that there was usually a supermarket within a 15 minute walk. In the country my parents had to drive to everything except the pub and playground, and deliberate effort was required to get more exercise.

This depends on how walkable your cities are, of course.